Hard drives utilizing magnetic data storage disks are used extensively in the computer industry. Each magnetic data storage disk in a hard drive has an associated slider which is used to magnetically read and write on a disk surface. In operation, the magnetic data storage disks are rotated and a slider is held very close to the surface of each disk surface. The motion of the disk past the slider allows data communication between the slider and disk surface.
The distance between the slider and disk must be accurately controlled. Typically, the slider is shaped to fly upon a cushion of moving air formed by the rapidly moving disk surface. The surface of the slider closest to the disk surface is called an air bearing surface. The air bearing surface has a shape which is designed to provide a small but stable flying height between the slider and disk. The slider must not touch the disk surface during operation because damage can result. Also, it is desirable to maintain as small a flying height as possible, because this increases the amount of data which can be stored. As flying height is reduced, it becomes increasingly difficult to maintain the flying height accuracy to the degree required for reliable recording and reading of data.
The shape of the slider has a substantial effect upon fly height. More specifically, the flying height is dependent upon the average curvature of the air bearing surface of the slider. The curvature of the air bearing surface is often affected by the manufacturing processes used to make the slider. Lapping of the slider (either the air bearing surface or a surface opposite to the air bearing surface) often causes stress variations in the slider which distort the shape of the air bearing surface. After lapping, it is almost always necessary (for high storage density applications) to adjust the curvature of the air bearing surface to a desired target curvature.
U.S. Pat. No. 5,266,769 to Deshpande et al. discloses a method of adjusting the curvature of the air bearing surface of a slider by scribing a back surface of the slider. The scribing removes material from the back surface, thereby releasing internal stress in the slider and controllably changing the curvature of the air bearing surface. Scribing may be performed with a laser, sandblasting tool or the like. A curvature measuring tool may monitor the curvature of the air bearing surface as material is removed, thereby providing feedback control if desired. A problem with the method of Deshpande is that sliders are most efficiently made in rows, and each slider in a row may have a different amount of stress. This means that each slider must have a different amount of material removed in order for the sliders to have the same air bearing surface curvature. Deshpande does not disclose a method for individually controlling the curvature of sliders in a row. Deshpande assumes that all sliders in a row require the same curvature adjustment. It would be an advance in the art to provide a row of sliders with individually controlled curvature.
Further, Deshpande does not disclose specific, advantageous methods of implementing curvature control. The curvature of a slider may only be changed `in one direction` by removal of material from the back side of the slider and so the target curvature must not be overstepped. Deshpande does not disclose a method for curvature adjustment which assures that the target curvature is not overstepped. Also, the changes in curvature caused by material removal from the back surface of the slider are not entirely predictable. When large changes in curvature are necessary, the final curvature of the slider may be rather inaccurate. Deshpande does not disclose a method which provides the same accuracy in curvature control for large and small curvature adjustments. Therefore, there are many improvements which can be made to the method of Deshpande.